Fuel supply system

ABSTRACT

A fuel supply system for mixture-compressing, externally ignited internal combustion engines is disclosed in which the influence of variable atmospheric pressure on the fuel-air mixture is compensated for by providing a secondary spring having pretension which is changeable in dependence on atmospheric pressure, this spring being fixed to a bellows which responds to atmospheric pressure. A primary control spring, together with the secondary spring, acts on a membrane which is part of a second pressure control valve.

United States Patent 1 1 1111 3,894,523 Stumpp July 15, 1975 FUEL SUPPLYSYSTEM 2,284 687 6/1942 Schirnanek .1 123/75 13 3,680,535 8/1972 Eckertet al l 123/[39 AW [75] lnvemo" Gerhard Stump!" Stuttgart 3330.1555/1973 Knapp 1, 123/139 AW Germany $835,828 9/1974 Knapp 123/139 AW [73]Assignee: Robert Bosch G.m.b.H., Stuttgart.

Germany Primary E.raminer-Wendell E. Burns Assistant ExaminerDavidReynolds [22] Flled; 1974 Attorney, Agent, or F1'rmEdwin E. Greigg [Zl]Appl. No: 465,504

{57} ABSTRACT [30) Foreign Application Priority D A fuel supply systemfor mixture-compressing, exter- May 29 973 Germany 2327295 nally ignitedinternal combustion engines is disclosed in which the influence ofvariable atmospheric pres- {521 Us CL H 123/139 123/75 D sure on thefuel-air mixture is compensated for by pro- [5]] 1m CL I k A i 7/20viding a secondary spring having pretension which is [58] Field ofSearch Aw 75 D changeable in dependence on atmospheric pressure, thisspring being fixed to a bellows which responds to [561 References Citedatmospheric pressure. A primary control spring. to-

gether with the secondary spring, acts on a membrane 9 UNITED STATESPATENTS which is part of a second pressure control valve. 1.72 .0429/1929 Junkers I23/75 D I 2,243,627 5/1941 Gregg 123/75 D 2 Claims, 1Drawmg Figure FUEL SUPPLY SYSTEM BACKGROUND OF THE INVENTION Thisinvention relates to a fuel supply system for mixture-compressingexternally ignited internal combustion engines. The present inventionrelates. more particularly to such fuel supply systems in which theinfluence of variable atmospheric pressure on the fuel-air mixture issubstantially fully compensated.

Fuel supply systems for mixture-compressing. extcr nally ignitedinternal combustion engines are known. in whose suction tube a measuringmember and an arbitrarily actuatable throttle flap are sequentiallydisposed. The measuring member is moved in proportion to the airquantity flowing through the suction tube and against a preferablyconstant resetting force. The measuring member displaces the movablepart of a quantity divider valve which meters an amount of fuelproportional to the air quantity. The resetting force is provided by apressurized fluid which acts continuously upon a control slide. atpreferably constant pressure. The pressurized fluid is delivered througha pressure line, the pressure of the fluid being changeable by means ofat least one pressure control valve which can be controlled independence on motor parameters. The pressure control valve includes aheatable control element operating in a temperature-dependent fashion.the control element being embodied as a bimetallic spring. connected toa heat conducting arm which is heated by a heating element immediatelyafter motor start-up. The heat conducting arm is thermally insulatedfrom the environment. The bimetallic spring acts in opposition to theforce of a control spring of the pressure control valve whenever thetemperatures are below the operating temperature of the motor.

In fuel supply systems of the type described above. there is the problemthat the fuel-air mixture is changed when the atmospheric pressurechanges. For a geodetic altitude difference of L000 meters, the airdensity is changed by approximately l percent. This leads to a change inthe fuel-air mixture by approximately percent.

SUMMARY OF THE INVENTION It is the principal object of the presentinvention to provide a fuel supply system of the kind described above inwhich the influence of atmospheric pressure on the fuel-air mixture issubstantially compensated.

The foregoing object, as well as others which are to become clear fromthe text below, is achieved according to the present invention in a fuelsupply system of the type described above by disposing. parallel to acontrol spring, a second spring, the pretension of the second springbeing changeable in dependence on the atmospheric pressure.

The disposition of the second spring parallel to the principal controlspring has the advantage that. during a failure of the member,preferably a bellows. which measures the atmospheric pressure. thepressure of the pressure medium is changed only by the amount requiredfor the equalization of the atmospheric pressure. Thus, the fuel supplysystem and the vehicle itself remain operational.

The degree of compensation can be influenced by a choice of the elasticproperties of the second spring.

An advantageous embodiment of the present invention is such that one endof the second spring is supported by a closed bellows which responds tothe atmospheric pressure. the other end being supported on a springsupport plate or cup. Because of the presence of a second spring. theclosed bellows is loaded only by a small force. The second spring issuitably so dimensioned that it is very nearly relaxed at sea levelbarometric pressure. but its pretension ought to be large enough so asto avoid wear and tear due to vibration.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is a view. partially insection. of an exemplary embodiment of a fuel supply system according tothe present invention in simplified formv DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENT In the fuel supply system shown. the combustion airflows in the direction of the arrow. shown farthest to the right.through an air filter I. through a suction tube sector 3. in which isdisposed a measuring member (air sensor) 4. further through a connectingtube 5. and a suction tube sector 6 containing an arbitrarily actuatablethrottle flap 7 and thence onto one or several cylinders (not shown) ofan internal combustion engine. The measuring member 4 embodied as aplate. is disposed in the suction tube sector 3 transverse to thedirection of air flow. and moves within the suction tube sector 3according to an approximately linear function of the air quantityflowing through the suction tube 3. 5. 6. wherein. if the resettingforce acting upon the measuring member 4 is constant. and if the airpressure prevailing ahead of the measuring member 4 is also constant.then the pressure prevailing between the measuring member 4 and thethrottle flap 7 is constant as well. The measuring member 4 directlycontrols a dividing and metering valve 8. A lever I0 is connected to themeasuring member 4 and is pivotablc about a pivot 9. Thus. settingmovements of the measuring member 4 are transmitted. via a projectionll, onto a control slide 12 of the metering valve 8. An end of thecontrol slide 12. which faces away from the projection II. is actuatedby a pressurized medium acting as a resetting force on the measuringmember 4.

Fuel supply takes place through a fuel pump [6 driven by an electricmotor 17. The fuel pump 16 pumps fuel from a container 36 and deliversit through a line 18 to the metering valve 8. From the line 18 fuelflows into a channel 19 within the housing of the metering valve 8. Thischannel 19 ends in an annular groove 20 which is connected. via bores2|. with an internal bore 22 which. together with reliefs in the controlslide 12, forms an annular groove 23. Depending on the position of thecontrol slide 12, the annular groove 23 more or less overlaps controlslits 24 through which the metered fuel can reach channels 25 which leadto the individual (not shown) injection valves of the internalcombustion engine. A portion ofthe fuel flows from the annular groove 20into a channel 26 and further to an annular groove 27 and. via bores 28,into a line 29 which communicates via a damping throttle 30 with apressure chamber 31 into which extends a face 13 of the control slide12.

The fuel serving as pressure medium flows through the line 29 to apressure control valve 32 which is a flat seat valve having a membrane33 and a fixed valve seat 34. Overflowing fuel flows without pressurethrough a line 35 back into the fuel container 36. The membrane 33 isloaded by a spring 37 whose pretension is adjustable depending oncharacteristic motor parameters. For this purpose, there exists athree-dimensional cam 38 rotatable in unison with the throttle flap 7and slidable axially depending on the reduced pressure prevailing in thesuction tube 3, 5, 6, downstream from the throttle flap 7. Thethree-dimensional cam 38 is mounted axially slidable on a shaft 39 fixedto the arbitrarily rotatable throttle flap 7. The rotation of the shaft39 is transmitted by an angular motion transfer lever 40 to thethree-dimensional cam 38 whose one face is attached to a membrane 41 ofapartial vacuum chamber 42.

The vacuum chamber 42 connects through a line 43 with a location withinthe suction tube 3, 5, 6, downstream from the throttle flap 7. lf thevacuum is sufficient. the cam 38 is axially displaced by the membrane 41in opposition to the force of a reset spring 44. A pin 45 follows thecam 38 and, via a spring support cup 46, acts upon the spring 37 whosepretension determines the pressure of the pressure fluid medium actingas the resetting force on measuring member 4.

Branching off from the line 29 is a second line leading to a secondpressure control valve 53 and further, via a return line 55 and withoutpressure, to the fuel container 36. The pressure control valve 53 makesit possible to control the pressure of the pressure fluid medium servingas the resetting force in a temperaturedcpendent and atmosphericpressure-dependent manner. The pressure control valve 53 is a flat seatvalve having a fixed valve seat 57 and a membrane 58. The membrane 58 isloaded in the direction of closure of the valve 53 by a control spring59 and a parallel second spring 63. The closing force of control spring59 is transmitted by a pin 60 lodged between the membrane 58 and thecontrol spring 59 and the parallel second spring 63. The pin 60 is heldat one end by a support bearing 61 on the membrane 58 and at its otherend by a spring retainer cup 62 which supports the control spring 59 andthe second spring 63. Opposing the spring retainer cup 62 is abimetallic spring 64 whose other end is secured on a bolt 65 pressedinto the housing of pressure control valve 53. The bimetallic spring 64is protected against heat loss by conduction to the housing of thepressure control valve 53 by an insulating member 66 disposed betweenthe bolt 65 and the bimetallic spring 64. Disposed parallel to thebimetallic spring 64 is a heat conductor arm 68 which is inheatconducting contact at the commmon fastening location shared with thebimetallic spring 64.

Mounted on the heat conducting arm 68 is an electric heating element 69.One electrical connection 70 of the electric heating element 69 isconnected to the positive pole of a battery or the like and the otherelectrical connection 72 can be connected with a ground contact 76 onthe housing via the free end 75 ofa bimetallic spring 73 additionallyfastened in the housing of the pressure control valve 53 in electricallyinsulated fashion. A parallel branch of the connection 72 leads to theground contact 76 through a resistor 74, which can be shunted, that isshorted out. by the bimetallic spring 73 whenever it contacts the groundcontact 76.

The end of the spring 63 opposite the spring retainer cup 62 issupported by a partially evacuated closed bellows 78 disposed in achamber 79 which communicates with the atmosphere through a channel 80.

The method of operation of the above-described fuel supply system is setforth in the paragraphs which follow.

When the internal combustion engine is running, the fuel pump 16, drivenby the electric motor 17, pumps fuel from the fuel container 36 throughthe line 18 to the metering valve 8. At the same time, the internalcombustion engine aspirates air through the suction tube 3, 5, 6, whichdisplaces the measuring member 4 from its normal, rest position.

Depending on the magnitude of this displacement of the measuring member4, the lever 10, fixedly connected with the measuring member 4, movesthe control slide 12, which opens a greater flow cross section of thecontrol slits 24. The amount of fuel which reaches the (not shown)injection valves through these changeable flow cross sections thuscorresponds to the instant position of the measuring member 4. A portionof the fuel flows from the annular groove 23 of control slide 12 throughthe channel 26 into the pressure chamber 31 where it impinges on theface 13 of the control slide 12 and it further flows through the line 29to the first pressure control valve 32 and also through the line 50 tothe second pressure control valve 53.

The direct and positive coupling of the measuring member 4 with thecontrol slide 12 results in a constant ratio of air quantity and fuelquantity, as long as the operational characteristics of these twoelements are sufficiently linear, which is a desired condition. Thus,the fuelair ratio would remain constant throughout the entireoperational domain of the internal combustion engine. Yet it isnecessary to make the fuel-air mixture richer or leaner. depending onthe operational conditions of the internal combustion engine. This isaccomplished through changing the resetting force acting on themeasuring member 4.

The measuring parameters for the load and the rpm of the engine are thethrottle flap position and the suction tube vacuum (reduced pressure),so that the resetting force is suitably changed depending on theseparameters. This is done in that, depending on the position of thethrottle flap 7 or depending on the magnitude of the pressure in thesuction tube 3, 5, 6, the force of the spring 37 in the first pressurecontrol valve 32 is changed by appropriate rotation or axialdisplacement of the three dimensional cam 38. For example, during fullload operation, if the throttle flap 7 is in a position in which thesuction tube 3, 5, 6, is fully open, then the maximum power is desiredwhich requires a relatively rich mixture. Since the pretension of thespring 37 of the first pressure control valve 32 determines the fuelpressure which acts on the face 13 of the control slide 12, it isnecessary to reduce somewhat the resetting force acting on the measuringmember 4, so that control slide 12 will be pushed into a position inwhich the control slits 24 are opened wider and a correspondingly largeramount of fuel is injected. Conversely, during partial load operation,the result is a relatively smaller deflection of the measuring member 4because of the relatively higher pressure acting on the face 13 ofcontrol slide 12', this leans out the fuel-air mixture.

In overrunning operation, when the pressure in the suction tube issharply reduced, the cam 38 is displaced against the force of the resetspring 44 so that the spring 37 of the first pressure control valve 32is further compressedv This increases the resetting force acting againstthe measuring member 4 which ensures that the measuring member 4 is notdisplaced and no fuel injection takes place in spite of small amounts ofleakage air" which might flow past the closed throttle flap 7. When themotor is warming up and until the operational motor temperature isreached, the mixture enrichment is determined in a temperature-dependentmanner by the control pressure influenced by the second pressure controlvalve 53. The control process is thus dependent on the externaltemperature when the motor is started. The control pressure isdetermined by the closing force exerted by the control spring 59 and thesecondary spring 63 onto the membrane 58. However. whenever thetemperature lies below the operational temperature of the internalcombustion engine. the bimetallic spring 64 acts on the spring retainercup 62 and opposes the control spring 59 and the secondary spring 63. Inthis way. the force transmitted to the membrane 58 is reduced. However,immediately after starting, the electric heating element 69 heats thebimetallic spring 64, and as a consequence. the force transmitted by thebimetallic spring 64 to the spring retainer cup 62 is reduced. The rateof this reduction depends on the amount of heat transmitted tobimetallic spring 64. It is desired that this reduction of the forcetransmitted by bimetallic spring 64 to the spring retainer cup 62 be aslinear as possible with respect to time. while corresponding to thewarm-up of the internal combustion engine, and. for this reason, theelectric heating element 69 is not directly connected with thebimetallic spring 64. but rather is disposed on the heat conducting arm68 which is capable of transmitting heat to the bimetallic spring 64only by heat conduction at the common fastening point. The amount of thebending of the heat conducting arm 68 towards or away from thebimetallic spring 64, depends on the amount of heat which is radiated tothe bimetallic spring 64 which can be changed. In this way. and in anadvantageous manner. one can obtain an adaptation of the tension vs.time behavior of the bimetallic spring 64 in the warmup phase so as tocorrespond to the warm-up characteristics of different engines. Thedesired basic pretension is achieved in that the bolt 65 is set todifferent depths within the housing of pressure control valve 53 or inthat the elastic characteristics of the control spring 59 are changed.

When the starting temperatures are below 0C., it is necessary to delayheating the bimetallic spring 64. This is done by means of the resistor74 in the current supply to the electric heating element 69. Duringnormal starting temperatures, the resistor 74 is shunted by thesupplementary bimetallic spring 73 so that the electric heating element69 is fully powered. In the drawing. the bimetallic spring 73 is shownin the position in which it shunts the resistor 74. Disposed parallel toand acting in the same direction as the control spring 59 is the secondspring 63 acting on the membrane 58, via the pin 60. The pretension ofthe secondary spring 63 can be changed, depending on the atmosphericpressure, in that its one end is supported tn the closed bellows 78located in the chamber 79 which communicates with atmospheric pressurethrough the channel 80.

This preferred embodiment of the invention permits compensation for theundesired fuel-air mixture change due to a change in the geodeticaltitude by varying the control pressure of the pressure fluid mediumadjusted by the pressure control valve 53 and hence by varying theresetting force acting on the measuring member 4. Thus, for example.when the atmospheric pressure decreases, the control pressure of thepressure fluid medium increases. If the bellows 78 fails. the controlpressure is changed only by this amount ofcorrection pressure,- whereasthe fuel supply system and hence the internal combustion engine itselfremain fully operational. The second spring 63 is so dimensioned that itis nearly relaxed at sea level barometric pressure.

lt is to be appreciated that the foregoing detailed description of theillustrated embodiment of a fuel supply system has been given by way ofexample. Numerous other embodiments and variants are possible withoutdeparting from the spirit and scope of the present invention. the scopebeing defined in the appended claims.

What is claimed is:

l. In a fuel supply system for mixture-compressing. externally ignitedinternal combustion engines. in whose suction tube a measuring memberand an arbitrarily actuatable throttle flap are sequentially disposedand wherein the measuring member is moved in proportion to air quantityflowing through the suction tube and against a preferably substantiallyconstant resetting force. which air quantity displaces a movable part ofa quantity divider valve which meters an amount of fuel proportional tothe air quantity and wherein the resetting force is provided by apressurized fluid which acts continuously upon a control slide with apreferably constant pressure which is delivered through a pressure line.and wherein the pressure ofthe fluid is changeable by at least onepressure control valve which can be controlled in dependence on at leastone motor operating parameter and which includes a heatable controlelement operating in a temperature-dependent manner. the control elementbeing embodied as a bimetallic spring connected to a heat conducting armwhich is heated by a heating element immediately after motor start-upand which is thermally insulated from the environment, the bimetallicspring acting in opposition to the force of a first control spring ofthe at least one pressure control valve whenever the temperature isbelow the motors operating temperature the improvement comprisingpressure sensitive means responsive to atmospheric pressure; and asecond control spring installed to act in parallel to said first controlspring. the pretension of said second spring being changeable independence on atmospheric pressure as sensed by said pressure sensitivemeans, said second spring being coupled to said pressure sensitivemeans.

2. A fuel supply system according to claim 1. further including a springretaining cup, and wherein one end of said second spring is supported bya bellows means which responds to atmospheric pressure and constitutessaid pressure sensitive means, and the other end of said second springbeing supported by said spring retaining cup.

1. In a fuel supply system for mixture-compressing, externally ignitedinternal combustion engines, in whose suction tube a measuring memberand an arbitrarily actuatable throttle flap are sequentially disposedand wherein the measuring member is moved in proportion to air quantityflowing through the suction tube and against a preferably substantiallyconstant resetting force, which air quantity displaces a movable part ofa quantity divider valve which meters an amount of fuel proportional tothe air quantity and wherein the resetting force is provided by apressurized fluid which acts continuously upon a control slide with apreferably constant pressure which is delivered through a pressure line,and wherein the pressure of the fluid is changeable by at least onepressure control valve wHich can be controlled in dependence on at leastone motor operating parameter and which includes a heatable controlelement operating in a temperature-dependent manner, the control elementbeing embodied as a bimetallic spring connected to a heat conducting armwhich is heated by a heating element immediately after motor start-upand which is thermally insulated from the environment, the bimetallicspring acting in opposition to the force of a first control spring ofthe at least one pressure control valve whenever the temperature isbelow the motor''s operating temperature the improvement comprisingpressure sensitive means responsive to atmospheric pressure; and asecond control spring installed to act in parallel to said first controlspring, the pretension of said second spring being changeable independence on atmospheric pressure as sensed by said pressure sensitivemeans, said second spring being coupled to said pressure sensitivemeans.
 2. A fuel supply system according to claim 1, further including aspring retaining cup, and wherein one end of said second spring issupported by a bellows means which responds to atmospheric pressure andconstitutes said pressure sensitive means, and the other end of saidsecond spring being supported by said spring retaining cup.